Before we discuss patterns in the casting process, a little history. The foundry industry dates back to early biblical times, (it is believed some 4,000 years BC) where they would pour castings out of gold, and then later copper, bronze, and tin.
One would assume that the casting images needed a pattern and in the early days the “pattern” was usually carved into an open stone or sand molds. More sophisticated.
Today’s modern foundries are not too far from the original metal casters. One difference, however, is that we now have many different ways to create the mold, and processes to melt and form the object.
Today, we will focus on the patterns for the sand method of molding, particularly the no-bake process that Quaker City Castings employs.
In order to create a casting, a pattern needs to be constructed that is an exact replica of the form that is wanted. In our application we use a few different materials when constructing the pattern and corresponding core boxes. The most widely used material is wood, generally sugar pine. Depending on the rate of usage of the pattern, harder woods can be used to allow for greater wearability, usually hard woods such as mahogany, maple, or the softer hardwood of poplar. In some cases, a metal or plastic pattern will be constructed to assure a long lifespan and the ability to hold tighter casting tolerances. On the rare occasion we will make the pattern out of foam that lasts only for one or two molds. The foam material is used to keep pattern costs to a minimum, when the cost of a permanent mold cannot be justified.
Once the pattern is constructed and delivered to the foundry, our in-house pattern shop will do a dimensional check to assure it meets the blue print specifications, and then gate and rig the equipment to fit one of our three molding lines. Along the way, many decisions must be made: what line does it fit, how many, if any, cores will be needed, what material is the metal to be cast so that the proper shrink factor can be used when constructing the equipment, and the degree of verifying and testing that might be requested after the casting is produced.
If the casting is not correct according to the drawing, or 3D model, the pattern maker is held responsible. Dimensional accuracy, construction, and expense are goals that we look for from the pattern shop.
The pattern is a vital leg of the foundry operation to help insure the production of a quality casting that is sound and visually acceptable. If the pattern equipment is rough and poorly constructed, the casting will have little to no chance in meeting our in-house and customer quality standards. The pattern makers we work with have a very high degree of foundry knowledge in both engineering and foundry practice.
The purchasing of the pattern equipment is always a necessary evil for the customer. So, it is one of our major duties to make sure the equipment that we supply addresses all of the customer’s requirements while giving them a world-class product at a competitive price, delivered on time.
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